This invention relates to a magnetic tape cassette, and more specifically to a magnetic tape cassette with an improved guard panel at the opening of the cassette housing.
Video tape cassettes are designed so that a portion of the magnetic tape is always drawn across the front opening of the cassette housing. A guard panel is openably provided there to protect the tape while the cassette is not in use. The panel is normally biased by spring means to the closing direction so that it always covers the opening when the cassette is not used.
Cassettes of this structure have had problems in common. When they are subjected to vibration or impact from the outside while in storage or in transportation, static electricity is generated by friction between the guard panel and the magnetic tape portion inside, or the panel is electrostatically charged by friction with some external object. In either case the charge draws dust onto the magnetic tape surface, with the possibility of subsequent dropouts, or attracts the tape to the inner surface of the guard panel.
As a countermeasure it has been proposed to form the guard panel and the opposite wall of the cassette housing from a plastic material mixed with an electrically conductive powder. The method has, however, had drawbacks of deformation during molding and some sacrifice of thermal resistance and mechanical strength.
It is an object of the present invention to provide a magnetic tape cassette of the type having a guard panel to expose or cover the front opening of the cassette housing, wherein the magnetic tape and the inner surface of the guard panel are protected from being electrostatically charged.
Another object of the invention is to prevent the electrostatic charging without the need of introducing an electrically conductive powder into the parts such as guard panel according to the prior practice which could cause deformation and reduced thermal resistance and mechanical strength of the magnetic tape cassette.
Yet another object of the invention is to achieve an antistatic effect by simple means at low cost.